These chelates may be used in the paper coating industry or as starch and protein insolubilizers, and in the petroleum industry for fracing petroleum bearing formations.
The chelates are used in both aqueous and non-aqueous solutions to retain metals in solution at high temperatures and over wide pH ranges and remaining compatible with other chemicals. Chelates can be of transition metals such as titanium, zirconium, copper, iron, and the like. Also aluminum and boron chelates react similar to transition metal chelates.
Particularly in the petroleum industry, chelates are used in cross-linking gels such as discussed by Almond in U.S. Pat. No. 4,477,360, Method and Compositions for Fracturing Subterranean Formations. The patentee discloses an aqueous gel containing a retarded cross-linking composition comprising a zirconium salt or chelate and a polyhydroxyl containing compounds. Typically referred to as polyols. Almond describes the useful polyol examples as glycerol, erythritol, threitol, ribitol, and others. Almond suggests that the polyhydroxyl containing compound useful in his process is admixed with an aqueous fluid and a cross-linking compound featuring zirconium chelates. He also points out that the constituents of the retarded cross-linking composition can be admixed in any order, in any conventional mixing apparatus. The gelling agents employed by Almond include gum guar, locust bean gum, karaya gum, sodium carboxymethylguar and several other compounds of guar.
Smeltz, U.S. Pat. No. 4,958,038 issued Sep. 18, 1990, describes a process which comprises combining glycerol, erythritol, arabitol, etc. and lactic acid, glycolic acid, malic acid, citric acid, tartaric acid, saccharic acid, gluconic acid, glyceric acid or mandelic acid to provide an aqueous solution of polyol and alpha-hydroxy carboxylic acid, and then at an alkaline pH of 10 or less reacting the solution with a titanium compound of an inorganic acid at an alpha-hydroxy carboxylic acid to titanium mol ratio between 0.5 to 1 and about 4 to 1 and a polyol to titanium mol ratio between about 0.25 to 1 and about 2 to 1. In fracing oil wells, Smeltz uses solvatable polysaccharides which include guar gum and locust bean gum, as well as other galactomannan and glucomannan gums, such as those derived from sennas, Brazilwood, Tera, Honey locust, Karaya gum and the like.
Hanlon et al, U.S. Pat. No. 4,460,751 describes a crosslinker which is made by preparing an alpha-hydroxy carboxylic acid solution, then adding a zirconium compound, e.g. zirconium oxychloride to form a second mixture, and finally adds the amine compound to the mixture. If zirconium carbonate is used, the zirconium carbonate is added to water to form a first mixture, next the amine compounded is added to form a second mixture, and finally the alpha-hydroxy carboxylic acid is added to the second mixture. Of course, Hanlon is not using chelates in his crosslinking composition.
Examples of the previous nonadvantageous methods of preparing zirconium chelates involves the use of dangerous solvents, such as ethers and alcohols, for producing zirconium triethanolamine chelates via zirconium n-propyl zirconate soluablized in n-propanol. This method involves the soluablization of zirconium tetrachloride which is also a dangerous chemical in n-propanol or ether followed by reacting it with triethanolamine. See Kucera, U.S. Pat. No. 4,692,254 describing such methods in detail.
Also aqueous chelates are produced through the separation of insoluble chelates as intermediates such as zirconium citrate, zirconium lactate and zirconium tartrate. This process generates effluents such as sodium sulphate, ammonium sulphate or other anions such as chlorides, nitrates, etc. See Van Mater, U.S. Pat. No. 2,498,514 describing such methods in more detail.
The prior methods of preparing zirconium chelates for preparation of solutions useful in fracing oil and gas strata have encountered such problems as low chemical yield, a need for an organic solvent which causes fire hazard and may produce toxic fumes or exhibits poor stability on aging and/or dilution, exposure to the atmospheric conditions, dilution with water, boiling and/or the addition of inorganic acids or bases. Also, such prior preparation methods have generated organic and/or inorganic effluent and/or solid waste.
The present invention relates to a new process for preparing zirconium chelate solutions which are stable on the addition of acids, bases, on boiling, at high dilution and/or aging; and therefor are useful in a wide range of industrial applications, especially in the areas of the paper coating industry and frac solutions for treating underground oil or gas bearing strata.